1. Field of the Invention
The present invention relates generally to a monopole antenna, and more particularly to a monopole antenna being used in an electronic device.
2. Description of the Prior Art
With the development of wireless communication, compact structure antennas are popular to be used in electronic devices. Several conventional compact structure antennas include multiple parts, usually occupying rekatively space, while the electronic device has compact structure. Thus, reducing the number of parts of antenna can significantly reduce the cost and suitable for used in the electronic device. TW Pat. No. 239677 describes a wide band monopole antenna. The monopole antenna comprises a grouding portion, a radiating portion located above the grouding portion and a feeder line. The grouding portion is rectangular and includes an up edge, a low edge, a grouding point and a short point. The radiating portion includes a first metal patch, a second metal patch and a short metal arm. The feeder line includes a center conductor and an external conductor. But the occupied space of the monopole antenna is too large to be assembled in an interior space of the electronic devices with compact structure.
Referring now to FIG. 1, a muti-band antenna 1′ is shown and includes an insulative substrate 10′, a first ground portion 20′, a second ground portion 50′, a low-frequency radiating portion 20′, a high-frequency radiating portion 30′, and a signal feeder cable 70′. The first ground portion 40′, the low-frequency radiating portion 40′, and the high-frequency radiating portion 30′ are made of sheet metal and are arranged on an upper surface of the insulative substrate 10′. The second ground portion 50′ is arranged on a lower surface of the insulative substrate 10′ opposite to the first ground portion 40′. The signal feeder cable 70′ comprises an inner core wire 71′ and a metal braiding layer 72′ respectively soldered onto the high-frequency radiating portion 30′ and the first ground portion 40′. The high-frequency radiating portion 30′ and the first ground portion 40′ are configured to cooperately define a resonating space 60′ therebetween. The low-frequency portion 20′ of the muti-band antenna 1′ is of trapezium shape and has difficulty to match impedance. The antenna with smaller size needs some special shape to achieve its impedance.
Hence, an improved antenna is desired to overcome the above-mentioned shortcomings of the existing antennas.